The understanding of the physiological functions of the human erythrocyte carbonic anhydrases rests on the complete characterization of their enzymatic catalysis of carbon dioxide hydration and dehydration. This characterization constitutes the main objective of this study. It includes studies designed to bridge remaining gaps in the available kinetics data, as well as studies designed to probe the relation between the three-dimensional structure of these enzymes and their catalytic functions. Questions regarding fundamental aspects of the extremely efficient catalytic mechanism of these enzymes are also investigated. Rapid kinetics techniques using stop-flow spectrophotometry are utilized in conjunction with active-site chemical modification and inhibition studies.